Method and apparatus for aerating organic waste material

ABSTRACT

A method and an apparatus is provided for aeration of organic material, wherein the organic material undergoes an aerobic composting process, such that air is caused to evenly penetrate the organic material. The organic material is first sealed in a vessel. Air is then delivered to the contents of the vessel such that an air pressure of from about 1 to about 1000 kPa above atmospheric pressure is maintained in the vessel. A pressure differential initially forms and is then allowed to equilibrate over a period of time, in which time air flows from areas of high pressure to areas of low pressure in the organic material thus ensuring that aeration is evenly distributed throughout the organic material.

FIELD OF THE INVENTION

[0001] The present invention relates to a method and apparatus foraeration of organic material, in particular organic waste, animalmanure, and biomass that is undergoing an aerobic composting process.

BACKGROUND OF THE INVENTION

[0002] Organic material such as biomass, organic waste and animal manuremay undergo aerobic composting to convert the organic material to abioactive stabilised end product that is useful as a soil-conditioner.Aerobic decomposition of organic material results from the metabolicactivity of aerobic microbial populations supported on the organicmaterial. An aerobic microbial population requires oxygen to maintainmetabolic activity. A constant supply of oxygen or air to the organicmaterial is crucial to maintain optimum microbial activity, thusensuring rapid biodegradation of organic matter.

[0003] There are several known methods by which the organic material canbe aerated whilst it is undergoing an aerobic composting process.

[0004] Air may be delivered to a volume of organic material contained ina treatment vessel by forced aeration wherein large volumes of air areblown or sucked into the vessel at low pressure. The success of theforced aeration method relies on the organic material having asufficient degree of porosity to allow air to penetrate the entirevolume of the organic material.

[0005] In practice, the forced aeration method has severaldisadvantages, notably as a result of the variable bulk density andporosity of the organic material in the treatment vessel. Air circulatesthrough the organic material and tends to travel a path of leastresistance through sections of the material having a low bulk densityand high porosity, thereby leaving the sections of material having ahigh bulk density and low porosity unaerated.

[0006] Large volumes of circulating air cool the organic materialproximal to regions of high air flow, thereby resulting in an uneventemperature distribution throughout the volume of organic material.Large volumes of circulating air also remove moisture from the material.It has been found that sophisticated odour scrubbing equipment isrequired to process the circulating air flows and prevent off-site odourimpacts. Further, blockage of any of the air delivery points results inlittle or no air distribution to the material proximal to the blockedair delivery point.

[0007] A method known as passive aeration may also be used to deliverair to the organic material for aerobic composting purposes. Organicmaterial is piled in such a manner that the temperature differencebetween the organic material and the ambient temperature creates aconvection current that draws fresh cool air into the pile.

[0008] The effectiveness of passive aeration is limited by the size ofthe pile as material which is located deep inside a large pile does nottend to receive a fresh air supply. Further, the composition of theorganic material is restricted to low bulk density materials as highbulk density materials do not have sufficient porosity to allowefficient air flow therethrough. Thus, passive aeration is generallyonly suitable for low bulk density materials such as shredded treewaste.

[0009] Regardless of whether the organic waste material undergoesaerobic decomposition in a treatment vessel or otherwise, the materialis typically mechanically agitated or turned at some stage in thecomposting process to distribute fresh air to the material. There are anumber of disadvantages associated with mechanically agitating orturning the material including the loss of heat and moisture from thematerial, the liberation of large volumes of volatile nitrogen early inthe composting process which reduces the nitrogen content of the finalproduct, and the release of odours from the material.

[0010] It is evident that the conventional methods of aeration oforganic material do not afford homogenous penetration of the organicmaterial by air whilst the conventional methods frequently result intemperature and humidity inhomogeneities within the organic material.

[0011] The present invention attempts to overcome, at least in part,some of the aforementioned disadvantages.

SUMMARY OF THE INVENTION

[0012] In accordance with a first aspect of the present invention thereis provided a method for aerating organic material undergoing an aerobiccomposting process, such that air is caused to evenly penetrate theorganic material, comprising the steps of:

[0013] a) sealing the organic material in a vessel;

[0014] b) delivering air to the contents of the vessel such that an airpressure of from about 1 to about 1000 kPa above atmospheric pressure ismaintained in the vessel.

[0015] In accordance with a second aspect of the present invention thereis provided an apparatus for aerating organic material undergoing anaerobic composting process, such that air is caused to evenly penetratethe organic material, comprising a vessel for receiving the organicmaterial, a means for sealing the vessel, and a means for delivering airto the contents of the vessel such that an air pressure of between about1 to about 1000 kPa above atmosphere is maintained in the vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will now be described, by way of exampleonly, with reference to the accompanying drawings, in which:

[0017]FIG. 1 is a schematic diagram of an apparatus for aerating organicmaterial in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0018] Referring to FIG. 1, there is shown an apparatus 10 for aeratingorganic material undergoing an aerobic composting process, such that airis caused to evenly penetrate the organic material. The apparatus 10includes a vessel 1 for receiving the organic material, a means forsealing the vessel 1, and a means for delivering air to the contents ofthe vessel 1 such that an air pressure of between about 1 to about 1000kPa above atmospheric pressure is maintained in the vessel 1.

[0019] The vessel 1 is an air tight pressurised vessel that is arranged,in use, to house organic waste material. The vessel 1 is constructedfrom a rigid, chemically inert material with good structural integrity,such as steel or concrete. The vessel 1 is arranged to operate in apressure range of from 1 to about 1000 kPa above atmospheric pressure.It is also envisaged that the vessel 1 will be arranged to facilitateconditions under which aerobic composting of the contents of the vessel1 will proceed.

[0020] The vessel 1 is provided with means for sealing the vessel 1 inorder to maintain an air pressure of from 1 to about 1000 kPa aboveatmospheric pressure in the vessel 1. The vessel 1 is also provided withan actuated valve 7 that is arranged, in use, to release and reduce airpressure inside the vessel 1.

[0021] The means for delivering air to the contents of the vessel 1includes an air compressor 5, a plurality of conduits 2 extending intoan interior of the vessel 1, and a manifold 4 in fluid communicationwith the air compressor 5 and the conduits 2. The conduits 2 are evenlyspaced and distributed throughout the interior of the vessel 1. Eachconduit 2 is provided with a plurality of apertures 3 extending alongthe length of the conduit 2. The manifold 4 facilitates airflow from theair compressor 5 to the conduits 2, and thence into the interior of thevessel 1 through the apertures 3 of the conduits 2.

[0022] In an alternative embodiment of the invention the means fordelivering air to the contents of the vessel 1 includes an aircompressor 5 in fluid communication with at least one inlet portprovided in a side of the vessel 1 to facilitate air flow from the aircompressor 5 to the interior of the vessel 1.

[0023] The vessel 1 is also provided with a means 6 for regulating airpressure within the vessel 1, and a means of measuring oxygenconcentration inside the vessel 1, such as an oxygen probe.

[0024] The operation of the apparatus 1 and the performance of themethod of the present invention will now be described with reference toFIG. 1.

[0025] The vessel 1 is loaded with organic material and then completelysealed. It will be understood that the term organic material encompassesbiomass, substantially solid organic waste such as municipal waste,animal manures, and a mixture thereof. Typically, the organic materialwill have been shredded and/or mixed, to afford a mixture with asubstantially homogenous porosity and bulk density, prior to it beingloaded into the vessel 1. It is also envisaged that the organic materialwill have been substantially evenly packed or distributed amongst theconduits 2 in the interior of the vessel 1.

[0026] Compressed air is supplied to the vessel 1 by the air compressor5. The compressed air is continuously delivered to the vessel 1 throughthe apertures 3 of the conduits 2 via the manifold 4 until the airpressure in the vessel 1 is increased to about 1 to about 1000 kPa aboveatmospheric pressure.

[0027] When compressed air is initially supplied to the vessel 1 and aninitial air pressure inside the vessel 1 is established, a first localair pressure at any one of the conduits 2 will be greater than a secondlocal air pressure at a location within the organic waste material,resulting in the formation of a pressure differential between any one ofthe conduits 2 and the location within the organic waste material. Overtime, air will flow from areas of higher pressure to those areas oflower pressure to equilibrate pressure within the vessel 1. In this way,air is caused to flow from the conduits 2 or inlet port of the vessel 1to every void within the organic waste material, thus ensuring evenpenetration of the organic waste material by air and a continuous supplyof oxygen to substantially all microbial populations resident andsupported by the organic waste material.

[0028] The period of time that is required to achieve pressureequalisation within the vessel, wherein every void within the organicwaste material has been completely aerated, is dependent on the bulkdensity and permeability of the organic waste material. The period oftime that is required to achieve pressure equalisation within the vessel1 can be shortened by increasing the air pressure within the vessel 1 toincrease the pressure differential between the conduits 2 and theorganic waste material, and so increase the rate of airflow from theconduits 2 to the organic waste material.

[0029] The concentration of oxygen in the vessel 1 is monitored eithercontinuously or intermittently by the oxygen probe. When the measuredoxygen concentration falls below a predetermined concentration, theactuated valve 7 is opened to release spent air from inside the vessel1, thus reducing the air pressure inside the vessel 1.

[0030] Fresh air may then be introduced into the vessel 1 as describedpreviously.

[0031] The present invention relies on the principle of airflow fromareas of high pressure to areas of low pressure to effect pressureequalisation within the vessel 1. The primary advantage of the presentinvention is that it ensures that an air supply is delivered evenlythroughout the organic waste material contained in the vessel 1.Further, it ensures that there is a substantially even temperaturedistribution throughout the organic waste material as the metabolicactivity of every microbial population is presumed to be operating underoptimum conditions. The present invention affords efficient air additionto reduce the volume of waste process air generated and subsequent odourproblems.

[0032] In comparison to other aeration methods, larger volumes oforganic waste material can undergo aerobic composting in the apparatusof the present invention because the means for delivering air to thecontents of the vessel causes the air to permeate all of the material inthe vessel. Similarly, organic waste material having a very low degreeof porosity or highly consolidated organic waste material can undergoaerobic composting in the apparatus of the present invention because themeans for delivering air to the contents of the vessel causes the air topermeate all of the material in the vessel. Aerobic composting oforganic waste material conducted in conjunction with the method andapparatus of the present invention can thus be successfully performedwithout the need for mechanical agitation.

[0033] Further, means are also provided for precise process controlthrough the regulation of air addition rates and pressures, and theremoval of spent air from the vessel prior to addition of oxygen richair. The present invention also significantly reduces moisture andtemperature loss during aeration of the organic waste material, thuscreating homogenous conditions for the microbial population within thematerial without the requirement for additional mechanical agitation orturning and further addition of moisture.

[0034] Modifications and variations as would be apparent to a skilledaddressee are deemed to be within the scope of the present invention

1. A method for aerating organic material undergoing an aerobiccomposting process, such that air is caused to evenly penetrate theorganic material, comprising the steps of: a) sealing the organicmaterial in a vessel; b) delivering air to the contents of the vesselsuch that an air pressure of from about 1 to about 1000 kPa aboveatmospheric pressure is maintained in the vessel.
 2. The methodaccording to claim 1, characterised in that a pressure differentialbetween an area of low pressure in the organic material and an area ofhigh pressure in the vessel is formed when air is delivered to thecontents of the vessel in step b), thus causing air to flow from thearea of high pressure in the vessel to the area of low pressure in theorganic material.
 3. The method according to claim 2, characterised inthat the pressure differential is allowed to equilibrate over a periodof time.
 4. The method according to claim 3, characterised in that theperiod of time is dependent on the bulk density and permeability of theorganic waste material.
 5. The method according to claim 3 or claim 4,characterised in that the period of time is shortened by increasing theair pressure within the vessel to increase the pressure differential,and so increase the rate of airflow from the area of high pressure tothe organic waste material.
 6. The method according to any one of claims1 to 5, characterised in that a concentration of oxygen in the vessel ismonitored either continuously or intermittently after step b).
 7. Themethod according to claim 6, characterised in that when the measuredoxygen concentration falls below a pre-determined concentration, spentair from inside the vessel is released from the vessel, thus reducingthe air pressure inside the vessel.
 8. The method according to claim 7,characterised in that after the air pressure inside the vessel isreduced, fresh air is then introduced into the vessel by repeating stepsa) and b).
 9. An apparatus for aerating organic material undergoing anaerobic composting process, such that air is caused to evenly penetratethe organic material, comprising a vessel for receiving the organicmaterial, a means for sealing the vessel, and a means for delivering airto the contents of the vessel such that an air pressure of between about1 to about 1000 kPa above atmosphere is maintained in the vessel. 10.The apparatus according to claim 9, characterised in that the means fordelivering air to the contents of the vessel comprises a compressed airsource in fluid communication with at least one inlet provided in thevessel.
 11. The apparatus according to claim 9 or claim 10,characterised in that the means for delivering air to the contents ofthe vessel comprises an air compressor, a plurality of conduitsextending into an interior of the vessel, and a manifold in fluidcommunication with the air compressor and the conduits.
 12. Theapparatus according to claim 11, characterised in that the conduits areevenly spaced and distributed throughout the interior of the vessel. 13.The apparatus according to claim 11 or claim 12, characterised in thateach conduit is provided with a plurality of apertures extending alongthe length of the conduit, such that the manifold facilitates airflowfrom the air compressor to the conduits, and thence into the interior ofthe vessel through the apertures of the conduits.
 14. The apparatusaccording to any one of claims 9 to 13, characterised in that theapparatus is further provided with a means for measuring oxygenconcentration inside the vessel.
 15. The apparatus according to any oneof claims 9 to 14, characterised in that the apparatus is furtherprovided with an actuated valve that is arranged, in use, to release andreduce air pressure inside the vessel.